Microtubules make up a diverse group of structures in the cell, ranging from the dynamic mitotic apparatus to the relatively stable nerve process. Little is known about how microtubules can achieve such a variety of properties or how their assembly is regulated in what has to be a temporally and spatially controlled manner. The goal of this proposal is to investigate the structure, function and expression of tau protein, a microtubule associated protein whose properties suggest that it might determine microtubule organization or subspecialization in the cell. Tau protein is a family of highly related phosphoproteins that promote in vitro assembly of microtubules and in vivo stabilization of microtubules. The specific aims of this work are: 1) to determine the complete amino acid sequence of two distinct mouse tau proteins, based on cDNA clones previously obtained from 6 day mice, and to identify areas of heterogeneity; 2) to determine whether the two heterogeneous tau cDNA clones originate from different genes or from a single gene by alternative processing of the mRNA. Genomic clones for tau will be isolated to address this point; 3) to determine the developmental expression of the two tau clones by using their unique regions in S1 analysis with mRNA from 5,10,15,20 day and adult mice brain; 4) to investigate the degree of conservation between tau proteins of different species, thus identifying domains common and possibly essential to tau proteins. The sequence of a rat tau cDNA clone will be determined and data from human tau cDNA will also be available for comparison; 5) to identify the microtubule binding domain in tau protein by expressing tau cDNA sequences in E. coli and subjecting the lysates to coassembly assays with microtubule protein; 6) to describe how tau proteins change in molecular weight and isoelectric point during development, using two dimensional gel analysis of 5,10,15,20 day and adult mice brain microtubule protein; 7) to obtain structural information about the remainder of the tau protein family by developing antibodies to specific tau sequences. In particular, an antibody to the area of heterogeneity between the two tau clones will be made. Lastly, because tau protein has been identified as a major antigenic determinant in neurofibrillary tangles of Alzheimer's disease, a neurodegenerative disorder of the brain, the study of tau protein will expand information on the composition of these lesions. Knowing the composition of the tangles is an important step in solving their origin.